This application is based on and claims the benefit of European Patent Application No. 00402299.2 filed Aug. 17, 2001, which is incorporated by reference herein.
The invention relates to an apparatus for producing annularly corrugated metal tubes, particularly the outer conductor of coaxial high-frequency cables, by means of a pressure roller.
Published Swiss application CH-A-275 509 discloses an apparatus for producing corrugated tubes with a pressure roller revolving around the workpiece, in which the corrugation is formed by teeth of the pressure roller (i.e., a toothed wheel). The pressure roller is rotatable about an axis which is at a 90xc2x0 angle to the longitudinal axis of the tube. Its axis of rotation, itself in a plane perpendicular to the longitudinal axis of the tube, revolves around the tube, which is being fed to the pressure roller, as the corrugation is being produced. The tube in turn rotates the pressure roller by its feed. This apparatus preferably includes three pressure rollers, which are offset by 120xc2x0 and engage the tube. The tips of the teeth located along the outer circumferences of the pressure rollers are concave and adapted to the tube diameter so that the pressure rollers form a self-contained forming tool.
With this configuration of the pressure rollers, it is not possible to produce tubes with a deep corrugation. To achieve a smaller distance between corrugations and a greater corrugation depth, it is therefore proposed to further form the corrugated tube by axial pressing. This results in an uncontrollable irregular shape of the corrugation, however. Another substantial drawback is that, due to the concave tips of the teeth and the large number of teeth, extremely high torsion forces act on the tube, which makes continuous production of thin-walled metal tubes difficult, if not impossible.
It is an object of the present invention to produce metal tubes with an annular corrugation, where the ratio of corrugation depth W1 to corrugation pitch W2 is greater than 0.3. Corrugation depth W1 is defined as the radial distance between a corrugation peak and the corrugation valley. Corrugation pitch W2 is the distance between two corrugation peaks. This extremely deep corrugation is to be produced without any additional measures, i.e., during the corrugation process.
This object is attained by an apparatus for producing annularly corrugated metal tubes, by means of at least one pressure roller revolving around a plain tube, wherein the corrugations are formed in the plain tube by the teeth of the pressure roller which is rotatable about an axis at a 90xc2x0 angle to the longitudinal tube axis, wherein the axis of rotation of the pressure roller, itself in a plane perpendicular to a longitudinal tube axis, revolves around the plain tube being fed to the pressure roller as the corrugations are produced, and wherein the plain tube in turn rotates the pressure roller by its feed. According to the invention, the tips of the teeth are flat, the tube is tightly guided in a guide bushing in front of and behind the engagement with the pressure roller, and the number of teeth ranges between 7 and 11, preferably between 8 and 10.
With the aid of the invention it has been possible to produce highly flexible metal tubes with deep corrugations in a single operation. Another essential advantage of the invention is that the corrugation, as viewed in the longitudinal direction of the metal tube, is uniform with respect to the corrugation depth and the corrugation pitch, so that the metal tubes are highly suitable as conductors of coaxial high-frequency cables and also as hollow conductors. There is no damage to the surface of the corrugated metal tube in the area of the corrugation valley or in the area of the corrugation sides.
Other advantageous features of the invention will be apparent from the detailed description below and the claims hereafter.